Isn't North Dakota one of the few States in the Union that bans robocalling???
If so, then we aren't going to get that many good polls out of ND....
Additionally, I have no reason to doubt that the AARP had a decent polling database, and considering that 33% of the entire population of the State is 50+, and 45% is 18-49 it actually represents likely at least 50% of the voting population in November '18, even in a relatively high voter turnout state....
Haven't looked at all of the polling details landlines vs cell phones, but I'm not expecting the 13% of the entire state population that is 18-25 to vote in especially high numbers in a Non-Presidential Year election....
People can talk about the roughnecks in the Petro boom parts of the State, which likely accentuate the 18-25 Yr Old chunk of State Population, but the reality is that many of them are essentially migratory workers that drift from Boom Town to Boom Town, don't establish deep local roots, and quite frankly include a high % of Latinos (Check out Eagle Ford Shale jobs in Texas), and generally aren't that likely to vote locally if at all....
The oldies are where it's at in North Dakota, and people are pissed at Trump's attempt to gut certain parts of ACA....
Johnny Cash: "Proud to be a Roughneck"
https://www.youtube.com/watch?v=2_H4w1Id7yE